Supposedly the number 1 cause of returns made to Glock are caused by over-lubing.
I haven't heard that. I have seen it cause problems, but I don't think it's the #1 cause.
In the picture below, you can see that besides all the Lubriplate, the Glock still has the copper anti-seize lube on it also:
Yeah, that's pretty much a ridiculous amount of lube. And most of it isn't even on surfaces where it can do any good. The plastic top of the frame and the bottom of the slide rails don't even really touch anything, other than perhaps some incidental contact between the two near the muzzle in some Glocks. If you want to put that much grease on your gun, and in places where it can't even provide lubrication, it probably won't hurt anything as long as you clean the gun frequently to remove the grease and fouling buildup. But you could run it with much less lube without causing any wear, without making cleanup as onerous, without using up as much lube, and without getting splattered with excess lubricant while shooting.
A little light grease on the inner grooves in the slide where the steel frame rails run, and on the steel frame rails is a good practice. It doesn't take much and it probably prevents wear a little better than oil since it tends to stay in place. I don't see any benefits to lubing the top of the frame and the bottom of the slide.
I'm a big fan of lubricating places where the gun needs it--not so much on just putting lots of lube everywhere.
As far as what to use, the key is more what not to use. You don't want to use a heavy/sticky grease, especially if you plan to use the gun in cold weather.
Most of the places that need lube in a gun don't need some super-special-heavy-duty lubricant. Just about anything will work. Where you want to specialize your lubricant is in terms of corrosion protection--that's where a premium product can really pay dividends in a firearm.